The goal of this project is to define the molecular mechanisms involved in the replication of enveloped RNA viruses and in particular, to understand factors which influence the regulation and expression of viral genetic information. The possible role of the viral RNA genome in directing virus assembly is currently being investigated in a system which uncouples murine leukemia virus RNA synthesis from terminal steps in virus maturation. The virus particles produced under these conditions resemble deletion mutants since they lack the 70S RNA genome and appear to contain only low molecular weight RNA species. In view of our recent results demonstrating that the defective virions contain normal amounts of all of the standard virus structural proteins and a fully functional reverse transcriptase, it will be of interest to further characterize virion RNA and to determine whether this RNA is derived from the host or whether a portion is virus-specific. BIBLIOGRAPHIC REFERENCES: Levin, J.G. and Rosenak, M.J.: Synthesis of murine leukemia virus proteins associated with virions assembled in actinomycin D-treated cells: evidence for persistence of viral messenger RNA. Proc. Natl. Acad. Sci. U.S.A. 73:1154-1158, 1976.